Surrounding monitoring apparatus

ABSTRACT

A surrounding monitoring apparatus obtains the position of a pedestrian contained in an image captured by a camera mounted on a vehicle on the basis of the position of the pedestrian in the image, and determines, on the basis of the obtained position, whether or not the possibility of collision with the pedestrian is high. In the apparatus, an error in extracting the pedestrian position may increase temporarily. In view of this, when the magnitude of change in a position correlation value representing the position of the pedestrian per a predetermined time (position change amount) exceeds a change amount upper limit value, the apparatus modifies the position correlation value such that the position change amount becomes equal to the change amount upper limit value and determines, on the basis of the modified position correlation value, whether or not the possibility of collision with the pedestrian is high.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority to Japanese Patent ApplicationNo. 2017-085150 filed on Apr. 24, 2017, which is incorporated herein byreference in its entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a surrounding monitoring apparatuswhich determines whether or not a pedestrian contained in a capturedimage of a region in a heading direction of a vehicle (hereinafter alsoreferred to as a “heading direction image”) is highly likely to collidewith the vehicle.

Description of the Related Art

One conventionally known surrounding monitoring apparatus of such a type(hereinafter also referred to as the “conventional apparatus”) has twocameras (so-called stereoscopic camera) which photograph a region in theheading direction of a vehicle. The conventional apparatus obtains apair of images at a proper timing through use of the two cameras. Theconventional apparatus extracts the contour of a pedestrian from each ofthe two images and obtains the distance between the vehicle and thepedestrian on the basis of the parallax of the contour of the pedestrianbetween the two images.

In addition, the conventional apparatus obtains the height of thepedestrian and the degree of opening of the legs of the pedestrian. Whenthe ratio (opening ratio) of the degree of opening of the legs to theheight is large, the conventional apparatus presumes that the “anglebetween the heading direction of the pedestrian and the headingdirection of the vehicle” is larger as compared with the case where theopening ratio is small, and determines that the pedestrian is highlylikely to cross the travel path of the vehicle (see, for example,Japanese Patent Application Laid-Open (kokai) No. 2007-264778).

Incidentally, in some cases, such a surrounding monitoring apparatus hasonly one camera for photographing the region in the heading direction ofthe vehicle (so-called monocular camera). In such a case, thesurrounding monitoring apparatus cannot obtain the distance between thevehicle and the pedestrian on the basis of the parallax. In view ofthis, such a surrounding monitoring apparatus may be designed to obtain(estimate) the distance between the vehicle and the pedestrian on thebasis of the position of the pedestrian on the image. Specifically, thesurrounding monitoring apparatus estimates that the higher the footposition of the pedestrian on the image, the larger the distance betweenthe vehicle and the pedestrian.

However, if the error involved in extraction of the contour of thepedestrian contained in the image increases and thus the error involvedin extraction of the foot position of the pedestrian in the imageincreases, the estimation error of the distance between the vehicle andthe pedestrian increases. For example, if a puddle is present on thewalking path of the pedestrian, the extraction error of the footposition may increases temporarily. Specifically, if an image of a footof the pedestrian and an image of the “foot reflected in the puddle”appear adjacently in the heading direction image, the surroundingmonitoring apparatus may extract the contour of the pedestrian in astate in which the apparatus erroneously recognizes the foot reflectedin the puddle as a portion of the pedestrian. In such a case, thesurrounding monitoring apparatus is highly likely to recognize the footon the image to be located at a position lower than the actual footposition.

In the case where a road sign on the walking path of the pedestrian andthe shoes of the pedestrian resemble each other in color, the extractionerror of the foot position may increase temporarily. Specifically, whenthe contour of the pedestrian is extracted, the road sign may beextracted as a portion of the pedestrian. In the case where the color ofthe shoes of the pedestrian and the color of a road resemble each other,the shoes of the pedestrian are recognized as a background, which raisesthe possibility that portions of the pedestrian covered by the shoes arenot extracted as a portion of the pedestrian.

If the error involved in the estimation of the distance between thevehicle and the pedestrian increases temporarily as a result of anincrease in the extraction error of the foot position as in theabove-described cases, it may become impossible to accurately determinewhether or not the possibility of collision with that pedestrian ishigh. In view of the forgoing, one object of the present invention is toprovide a surrounding monitoring apparatus which can accuratelydetermine whether or not the possibility of collision of a vehicle witha pedestrian is high irrespective of a temporary increase in the errorinvolved in extraction of the contour of the pedestrian contained in animage captured by a single camera.

SUMMARY OF THE INVENTION

A vehicle surrounding monitoring apparatus which achieves theabove-described object (hereinafter also referred to as the “apparatusof the present invention”) includes one camera, a pedestrian positionobtainment section, a position processing section, and a collisiondetermination section.

The camera (rear camera 45) is mounted on a vehicle (10) and obtains aheading direction image by photographing a region in a heading directionof said vehicle.

Said pedestrian position obtainment section executes a positionobtainment process every time a predetermined time interval (timeinterval Ts) elapses so as to obtain a position correlation value(vertical position Dx and horizontal position Dy) representing aposition of a pedestrian with respect to said vehicle on the basis of aposition (image vertical position Px and image horizontal position Py)of said pedestrian in said heading direction image (step 825 of FIG. 8).

Said position processing section operates every time said positioncorrelation value is obtained so as to determine a position processedvalue (processed vertical position Dpx and processed horizontal positionDpy) on the basis of said obtained position correlation value (step 830of FIG. 8 and FIG. 9).

Said collision determination section determines, at a first time pointwhen said position processed value is newly determined, whether or not apossibility of collision of said vehicle with said pedestrian is high,on the basis of said newly determined position processed value (step 855of FIG. 8).

When said position correlation value obtained at said first time pointis larger than a first specific value obtained by adding a predeterminedfirst limit value (first vertical limit value Dxth1 and first horizontallimit value Dyth1) to said position processed value (previous verticalposition Dox and previous horizontal position Doy) at a second timepoint which precedes said first time point by said interval time, saidposition processing section determines said position processed value atsaid first time point to be equal to said first specific value (steps915 and 940 of FIG. 9).

When said position correlation value obtained at said first time pointis smaller than a second specific value obtained by subtracting apredetermined second limit value (second vertical limit value Dxth2 andsecond horizontal limit value Dyth2) from said position processed valueat said second time point, said position processing section determinessaid position processed value at said first time point to be equal tosaid second specific value (steps 925 and 950 of FIG. 9).

When said position correlation value obtained at said first time pointis equal to or smaller than said first specific value and is equal to orlarger than said second specific value, said position processing sectiondetermines said position processed value at said first time point to beequal to said position correlation value obtained at said first timepoint (steps 930 and 955 of FIG. 9).

In general, the moving speed (walking speed) of the pedestrian isrelatively low. Therefore, the magnitude of a “position difference valuewhich is a value obtained by subtracting the position correlation valueat the first time point from the position processed value at the secondtime point” does not become excessively large. Meanwhile, as describedabove, when the foot position extraction error becomes largetemporarily, the magnitude of the position difference value becomeslarge. In view of this, when the magnitude of the position differencevalue becomes larger than the first limit value or the second limitvalue, the apparatus of the present invention determines that atemporary increase in the foot position extraction error has occurred.

In such a case, the above-mentioned position processing sectiondetermines the position processed value to be equal to the firstspecific value or the second specific value, and the above-mentionedcollision determination section determines, on the basis of the positionprocessed value, whether or not the possibility of collision of thevehicle with the pedestrian is high. Therefore, in the case of theapparatus of the present invention, even when the error in extraction ofthe contour of the pedestrian contained in the heading direction imagecaptured by the camera becomes large temporarily, the position of thepedestrian recognized by the apparatus of the present invention isprevented from greatly deviating from the actual position of thepedestrian. Therefore, the apparatus of the present invention canaccurately determine whether or not the possibility of collision of thevehicle with the pedestrian is high even when the error in extraction ofthe contour of the pedestrian contained in the image captured by thesingle camera increases temporarily.

The above-mentioned collision determination section may determine thatthe possibility of collision of the vehicle with the pedestrian is highif the magnitude of an acceleration (necessary acceleration) requiredfor the vehicle to stop before a position corresponding to the positionprocessed value (i.e., the estimated position of the pedestrian withrespect to the vehicle) is larger than a predetermined value.Alternatively, the collision determination section may determine thatthe possibility of collision of the vehicle with the pedestrian is highif the time (time to collision) until the vehicle collides with thepedestrian under the assumption that the travel speed of the vehicle isconstant is shorter than a predetermined time. When the collisiondetermination section determines that the possibility of collision ofthe vehicle with the pedestrian is high, the apparatus of the presentinvention may notify (warn) the driver of the vehicle that thepossibility of collision with the pedestrian is high, or may cause abraking apparatus of the vehicle to generate a braking force to therebystop the vehicle.

In one mode of the apparatus of the present invention, said positionprocessing section changes at least one of said first limit value andsaid second limit value such that said at least one limit valueincreases with the magnitude of travel speed of said vehicle.

In the case where the moving speed of the pedestrian does not change,the position difference value increases with the travel speed of thevehicle. In the present mode, the first limit value and/or the secondlimit value is set to larger values in accordance with an increase inthe position difference value due to an increase in the magnitude of thetravel speed. Therefore, according to the present mode, thedetermination as to whether or not the possibility of collision of thevehicle with the pedestrian is high can be made accurately irrespectiveof the magnitude of the travel speed of the vehicle.

In another mode of the apparatus of the present invention,

said camera is configured to obtain said heading direction image suchthat the longer the distance between said vehicle and an object presentin said heading direction, the higher the position (image verticalposition Px) of said object in said heading direction image; and

said pedestrian position obtainment section is configured to obtain, assaid position correlation value, a value (vertical position Dx)representing the distance between said vehicle and said pedestrian insaid vehicle heading direction, and is configured to obtain saidposition correlation value such that the higher the position of a footof said pedestrian in said heading direction image, the greater saiddistance represented by said position correlation value.

Since the apparatus of the present invention includes one camera, theapparatus cannot obtain the distance between the vehicle and thepedestrian on the basis of parallax as in the case of the conventionalapparatus. However, according to the present mode, the positioncorrelation value can be obtained by simple processing on the basis ofone heading direction image captured by one camera.

In still another mode of the apparatus of the present invention, saidcollision determination section is configured to employ, as a necessarycondition for determining that the possibility of collision of saidvehicle with said pedestrian is high, a condition that said positionprocessed value is a value representing a position within a path region(Ap) through which said vehicle is expected to pass as a result oftraveling (condition (A) and step 840 of FIG. 8).

If the position of the pedestrian represented by the position processedvalue determined by the position processing section is contained in thepath region, when the vehicle travels, the vehicle is likely to collidewith the pedestrian. For example, the collision determination sectioncan determine whether or not the possibility of collision is high byemploying the above-described necessary acceleration or time tocollision for that pedestrian. Therefore, according to the present mode,it is possible to accurately determine whether or not the possibility ofcollision of the vehicle with the pedestrian is high.

In still another mode of the apparatus of the present invention, saidcollision determination section is configured to estimate, on the basisof said position processed value, a predicted position (predictedvertical position Dfx and predicted horizontal position Dfy) which isthe position of said pedestrian with respect to said vehicle afterelapse of a predetermined prediction time (prediction time Tf), and toemploy, as a necessary condition for determining that the possibility ofcollision of said vehicle with said pedestrian is high, a condition thatsaid predicted position is a position within a path region (Ap) throughwhich said vehicle is expected to pass as a result of traveling(condition (B) and step 840 of FIG. 8).

For example, it is possible to calculate a value (speed correlationvalue) which correlates with the moving speed of the pedestrian bydividing the position difference value by the above-mentioned timeinterval and obtain the predicted position on the basis of the speedcorrelation value. Even when a pedestrian is present outside the pathregion at the present point in time, after that, the pedestrian mayenter the path region and the vehicle may collide with the pedestrian.According to the present mode, it is possible to accurately determinewhether or not the possibility of collision of the vehicle with a“pedestrian present outside the path region at the present point intime” is high.

In the above description, in order to facilitate understanding of thepresent invention, the constituent elements of the inventioncorresponding to those of an embodiment of the invention which will bedescribed later are accompanied by parenthesized names and/or symbolswhich are used in the embodiment; however, the constituent elements ofthe invention are not limited to those in the embodiment defined by thenames and/or the symbols. Other objects, other features, and attendantadvantages of the present invention will be readily appreciated from thefollowing description of the embodiment of the invention which is madewith reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a vehicle (present vehicle) whichincludes a surrounding monitoring apparatus according to an embodimentof the present invention (present monitoring apparatus);

FIG. 2 is a block diagram of the present monitoring apparatus;

FIG. 3 is an illustration showing an example of a pedestrian appearingon a heading direction image;

FIG. 4 is a graph showing the relation between speed of the presentvehicle and distance threshold;

FIG. 5 is a graph showing the actual vertical position of a pedestrianwhich changes with elapse of time, the vertical position obtained by aposition obtainment process, and the processed vertical positionobtained by a position correction process;

FIG. 6 is an illustration showing a path region for the case where thepresent vehicle moves straight backward;

FIG. 7 is an illustration showing a path region for the case where thepresent vehicle moves backward while turning;

FIG. 8 is a flowchart representing a collision avoidance control routineexecuted by the present monitoring apparatus; and

FIG. 9 is a flowchart representing a position correction process routineexecuted by the present monitoring apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A surrounding monitoring apparatus according to an embodiment of thepresent invention (hereinafter also referred to as the “presentmonitoring apparatus”) will be described with reference to the drawings.The present monitoring apparatus is applied to a vehicle 10 shown inFIG. 1. FIG. 2 shows a block diagram of the present monitoringapparatus. The present monitoring apparatus includes a “surroundingmonitoring ECU 20, an engine ECU 31, and a brake ECU 32” each of whichis an electric control unit (ECU).

The surrounding monitoring ECU 20 includes a CPU, a ROM, and a RAM. TheCPU performs data reading, numerical computation, computation resultoutput, etc. by repeatedly executing predetermined programs (routines).The ROM stores the programs executed by the CPU, lookup tables (maps),etc. The RAM stores data temporarily.

Like the surrounding monitoring ECU 20, each of the engine ECU 31 andthe brake ECU 32 includes a CPU, a ROM, and a RAM. These ECUs canperform data communication (can exchange data) with one another througha CAN (controller area network) 34. In addition, through the CAN 34,each ECU can receive from “other ECUs” output values of sensorsconnected to the other ECUs.

The surrounding monitoring ECU 20 is connected to a shift positionsensor 41, a vehicle speed sensor 42, an acceleration sensor 43, asteering angle sensor 44, a rear camera 45, an input output device 46,and speakers 47.

The shift position sensor 41 outputs to the surrounding monitoring ECU20 a signal representing a travel mode (shift position) of the vehicle10 selected by a driver's operation of a shift lever (not shown). Shiftpositions include a parking (P) range for parking, a drive (D) range forforward travelling, a reverse (R) range for backward travelling, aneutral (N) range for interrupting the transmission of torque from anengine 62 which is a drive source of the vehicle 10 to drive wheels (notshown), and a low (L) range which is higher in gear ratio Rg than thedrive (D) range. The gear ratio Rg is the ratio of the rotational speedof the engine 62 to the rotational speed of the drive wheels.

The vehicle speed sensor 42 outputs to the surrounding monitoring ECU 20a signal representing the magnitude of the speed Vs of the vehicle 10(hereinafter referred to as the “vehicle speed Vs”). In the case wherethe shift position is a position other than the reverse (R) range, thevehicle speed Vs is represented by a positive value. Meanwhile, in thecase where the shift position is the reverse (R) range, the vehiclespeed Vs is represented by a negative value.

The acceleration sensor 43 outputs to the surrounding monitoring ECU 20a signal representing the acceleration As of the vehicle 10 in thelongitudinal direction (the amount of change in the vehicle speed Vs perunit time).

The steering angle sensor 44 is disposed on a steering shaft (not shown)connected to a steering wheel 51. The steering angle sensor 44 outputsto the surrounding monitoring ECU 20 a signal representing a steeringangle θs which is the rotational angle of the steering shaft of thesteering wheel 51. The steering angle θs becomes “0” when the steeringwheel 51 is located at its neutral position. The steering angle θsassumes a positive value when the steering wheel 51 is rotated clockwisefrom the neutral position and assumes a negative value when the steeringwheel 51 is rotated counterclockwise from the neutral position.

The rear camera 45 is disposed at a central portion of the rear end ofthe vehicle 10. The rear camera 45 captures an image of a region locatedrearward of the vehicle 10 (hereinafter also referred to as the “headingdirection image” because the image is an image of a region which islocated in the heading direction of the vehicle 10 when the vehicle 10moves backward) and outputs a signal representing the heading directionimage to the surrounding monitoring ECU 20.

The angle of view (field of view) of the rear camera 45 in thehorizontal direction is equal to a range represented by an angle (anangle less than 180°) formed between a straight line RL and a straightline RR shown in FIG. 1. The angle between the straight line RL and acenter axis Cs which passes through the center of the vehicle 10 in thevehicle width direction thereof and extends in the straight forwarddirection of the vehicle 10 is θw. In addition, the angle between thestraight line RR and the center axis Cs is θw. Accordingly, a subjectwhich is located rearward of the vehicle 10 and located on the centeraxis Cs appears at the center of the heading direction image in thelateral direction.

Notably, as shown in FIG. 1, the longitudinal direction of the vehicle10 (direction parallel to the center axis Cs) is defined as an x axis,and the lateral direction of the vehicle 10 (vehicle width direction) isdefined as a y axis. The lateral center of the rear end of the vehicle10 is the origin where x=0 and y=0. The x coordinate value assumes apositive value on the side of the origin toward the backward directionof the vehicle 10 and assumes a negative value on the side of the origintoward the forward direction of the vehicle 10. The y coordinate valueassumes a positive value on the left side with respect to the headingdirection of the vehicle 10 moving backward and assumes a negative valueon the right side with respect to the heading direction of the vehicle10 moving backward. In the present specification, the direction in whichthe vehicle 10 turns as a result of backward movement of the vehicle 10in a state in which the steering angle θs is positive will be referredto as the “leftward direction.” Meanwhile, the direction in which thevehicle 10 turns as a result of backward movement of the vehicle 10 in astate in which the steering angle θs is negative will be referred to asthe “rightward direction.”

The input output device 46 is disposed on the dashboard of the vehicle10. The input output device 46 includes a display unit (liquid crystaldisplay). Characters, figures, etc. displayed on the display unit of theinput output device 46 are controlled by the surrounding monitoring ECU20. The display unit of the input output device 46 also functions as atouch panel. Accordingly, a driver can send instructions to thesurrounding monitoring ECU 20 by touching the display unit.

The speakers 47 are respectively disposed inside the left and rightfront doors (not shown) of the vehicle 10 (within the vehiclecompartment). The speakers 47 can produce sounds such as a warning soundand a voice message in accordance with instructions from the surroundingmonitoring ECU 20.

The engine ECU 31 is connected to a plurality of engine sensors 61 andreceives detection signals from these sensors. The engine sensors 61detect the operation state quantities of the engine 62. The enginesensors 61 include an accelerator pedal operation amount sensor, athrottle valve opening sensor, an engine speed sensor, an intake airamount sensor, etc.

Further, the engine ECU 31 is connected to engine actuators 63, such asa throttle valve actuator and a fuel injection valve, and a transmission64. The engine ECU 31 changes the drive torque Tq generated by theengine 62 and the gear ratio Rg of the transmission 64 by controllingthe engine actuators 63 and the transmission 64. Thus, the engine ECU 31adjusts the drive force of the vehicle 10, to thereby control theacceleration As. Meanwhile, the surrounding monitoring ECU 20 drives theengine actuators 63 and the transmission 64 by sending instructions tothe engine ECU 31, to thereby change the driving force of the vehicle10.

The brake ECU 32 is connected to a plurality of brake sensors 65 andreceives detection signals from these sensors. The brake sensors 65detect parameters used for controlling an unillustrated “brake(hydraulic frictional brake) mounted on the vehicle 10.” The brakesensors 65 include an operation amount sensor for detecting theoperation amount of a brake pedal (not shown), wheel speed sensors fordetecting the rotational speeds of the wheels, etc.

Further, the brake ECU 32 is connected to a brake actuator 66. The brakeactuator 66 is a hydraulic control actuator. The brake actuator 66 isprovided in a hydraulic circuit extending between a master cylinderwhich pressurizes hydraulic oil by using the depressing force applied tothe brake pedal and the friction brake including well-known wheelcylinders provided in the wheels. The hydraulic circuit, the mastercylinder, and the friction brake are not shown in the drawings. Thebrake actuator 66 controls the oil pressure supplied to the wheelcylinders. The brake ECU 32 generates a brake force (frictional brakeforce) Bf applied to the wheels, by driving the brake actuator 66, so asto control the acceleration As of the vehicle 10 (specifically, decreasethe magnitude |Vs| of the vehicle speed Vs). Meanwhile, the surroundingmonitoring ECU 20 drives the brake actuator 66 by sending an instructionto the brake ECU 32, to thereby change the braking force Bf.

Collision Avoidance Control

In the case where the vehicle 10 moves backward, if the possibility ofcollision with a pedestrian present in the backward direction of thevehicle 10 is high, the surrounding monitoring ECU 20 executes collisionavoidance control for notifying (warning) the driver of the vehicle 10of the possibility of collision and causing the brake actuator 66 togenerate the braking force Bf, to thereby stop the vehicle 10.

In order to determine whether or not the possibility of collision of thevehicle 10 with the pedestrian is high, the surrounding monitoring ECU20 obtains “the vertical position Dx which is the x coordinate value”and “the horizontal position Dy which is the y coordinate value” of thepedestrian contained in the heading direction image, every time apredetermined time interval Ts (fixed value) elapses. Specifically, thesurrounding monitoring ECU 20 executes a “position obtainment process”of estimating the vertical position Dx and the horizontal position Dy onthe basis of the position of the pedestrian in the heading directionimage. For convenience sake, the vertical position Dx and the horizontalposition Dy will also be referred as a “position correlation value.”

At the time of execution of the position obtainment process, thesurrounding monitoring ECU 20 searches a “portion of the headingdirection image, which portion is similar to any of many pedestriantemplates (pedestrian patterns) stored in advance.” If a portion of theheading direction image which is similar to one of the pedestriantemplates (namely, a pedestrian in the heading direction image) isfound, the surrounding monitoring ECU 20 extracts the contour of “thepedestrian in the heading direction image” which corresponds to thatpedestrian template. Namely, the surrounding monitoring ECU 20 extractsthe contour of the pedestrian contained in the heading direction imageby means of pattern matching.

After extraction of the contour of the pedestrian contained in theheading direction image, the surrounding monitoring ECU 20 obtains animage vertical position Px and an image horizontal position Py whichrepresent the foot position of the pedestrian in the heading directionimage. FIG. 3 shows a heading direction image IM from which the contourof a pedestrian 81 (which is also shown in FIG. 1) has been extracted.As shown in FIG. 3, the image vertical position Px is the length in thevertical direction between the lower end IMk of the heading directionimage IM and a position corresponding to the lower end Fp of thepedestrian 81 in the heading direction image. Meanwhile, the magnitude|Py| of the image horizontal position Py is the length in the lateraldirection between the lateral center of the pedestrian 81 in the headingdirection image and a center line Pc which is the lateral center of theheading direction image.

The value of the image vertical position Px is “0” when the lower end ofthe pedestrian is located at the lower end of the heading directionimage and the value changes such that the higher the lower end of thepedestrian in the heading direction image, the greater the value of theimage vertical position Px. Meanwhile, the value of the image horizontalposition Py is “0” when the lateral center of the pedestrian is locatedon the center line Pc. When the lateral center of the pedestrian islocated on the left side of the center line Pc, the image horizontalposition Py assumes a positive value, and the value of the imagehorizontal position Py changes such that the greater the leftwardseparation of the lateral center of the pedestrian from the center linePc, the greater the value of the image horizontal position Py. Inaddition, when the lateral center of the pedestrian is located on theright side of the center line Pc, the image horizontal position Pyassumes a negative value, and the magnitude |Py| of the image horizontalposition Py changes such that the greater the rightward separation ofthe lateral center of the pedestrian from the center line Pc, thegreater the magnitude |Py|.

The surrounding monitoring ECU 20 obtains (estimates) the verticalposition Dx and the horizontal position Dy from the image verticalposition Px and the image horizontal position Py. More specifically, thegreater the actual vertical position Dx, the greater the image verticalposition Px. In addition, the greater the magnitude |Dy| of the actualhorizontal position Dy, the greater the magnitude |Py| of the imagehorizontal position Py. Furthermore, when the magnitude |Dy| of thehorizontal position Dy is constant, the greater the vertical positionDx, the smaller the magnitude |Py| of the image horizontal position Py.

In view of this, the surrounding monitoring ECU 20 obtains the verticalposition Dx by applying the image vertical position Px to a “lookuptable which defines the relation between the image vertical position Pxand the vertical position Dx” which is stored in advance. In addition,the surrounding monitoring ECU 20 obtains the horizontal position Dy byapplying the image vertical position Px and the image horizontalposition Py to a “lookup table which defines the relation between the“image vertical position Px and the image horizontal position Py” andthe horizontal position Dy” which is stored in advance.

Incidentally, if the error in extraction of the contour of thepedestrian appearing in the heading direction image is large, the errorcontained in the combination of the image vertical position Px and theimage horizontal position Py becomes large, so that the error containedin the combination of the vertical position Dx and the horizontalposition Dy becomes large.

For example, in the case where a puddle is present on a walking path ofthe pedestrian and therefore, adjacent to an image of a foot of thepedestrian, an image of the “foot reflected in the puddle” appears inthe heading direction image, the error in the extraction of the contourof the pedestrian may become large temporarily. Also, in the case wherea road sign on the walking path of the pedestrian and the shoes of thepedestrian resemble each other in color, the error in the extraction ofthe contour of the pedestrian may become large temporarily.

In view of this, the surrounding monitoring ECU 20 executes a “positioncorrection process” so as to accurately determine whether or not thepossibility of collision of the vehicle 10 with the pedestrian is higheven when the error in the extraction of the contour of the pedestrianmay become large temporarily. The surrounding monitoring ECU 20 obtainsthe processed vertical position Dpx and the processed horizontalposition Dpy by the position correction process. By a process to bedescribed later, the surrounding monitoring ECU 20 accurately determineswhether or not the possibility of collision of the vehicle 10 with thepedestrian is high on the basis of the processed vertical position Dpxand the processed horizontal position Dpy. For convenience sake, each ofthe processed vertical position Dpx and the processed horizontalposition Dpy will also be referred to as a “position processed value.”

The position correction process will be described. In the followingdescription, the difference between the vertical position Dx obtained bythe position obtainment process executed latest and a previous verticalposition Dox which is the processed vertical position Dpx obtained whenthe position obtainment process and the position correction process wereexecuted last time will also be referred to as a vertical positiondifference ΔDx (i.e., ΔDx=Dx−Dox). Meanwhile, the difference between thehorizontal position Dy obtained by the position obtainment processexecuted latest and a previous horizontal position Doy which is theprocessed horizontal position Dpy obtained when the position obtainmentprocess and the position correction process were executed last time willalso be referred to as a horizontal position difference ΔDy (i.e.,ΔDy=Dy−Doy).

In general, since the moving speed (walking speed) of the pedestrian isrelatively low, the magnitude of the vertical position difference ΔDxnormally does not assume a large value. In view of this, when thesurrounding monitoring ECU 20 executes the position correction process,if the vertical position difference ΔDx is larger than a predeterminedfirst vertical limit value Dxth1 (i.e., ΔDx>Dxth1>0), the surroundingmonitoring ECU 20 determines the processed vertical position Dpx to beequal to a value obtained by adding the first vertical limit value Dxth1to the previous vertical position Dox (i.e., Dpx←Dox+Dxth1). Forconvenience sake, the value obtained by adding the first vertical limitvalue Dxth1 to the previous vertical position Dox will also be referredto as a “first specific value.”

If the vertical position difference ΔDx is smaller than a value (−Dxth2)obtained by multiplying a predetermined second vertical limit valueDxth2 by “−1” (i.e., ΔDx<−Dxth2<0), the surrounding monitoring ECU 20determines the processed vertical position Dpx to be equal to a valueobtained by subtracting the second vertical limit value Dxth2 from theprevious vertical position Dox (i.e., Dpx←Dox−Dxth2). For conveniencesake, the value obtained by subtracting the second vertical limit valueDxth2 from the previous vertical position Dox will also be referred toas a “second specific value.”

If the vertical position difference ΔDx is equal to or smaller than thefirst vertical limit value Dxth1 and is equal to or larger than thevalue obtained by multiplying the second vertical limit value Dxth2 by“−1” (i.e., −Dxth2≤ΔDx≤Dxth1), the surrounding monitoring ECU 20determines the processed vertical position Dpx to be equal to thevertical position Dx (i.e., Dpx←Dx).

Namely, if the magnitude of the vertical position difference ΔDx islarge, the surrounding monitoring ECU 20 determines that the error ofthe vertical position Dx has increased temporarily and uses thecorrected value as the processed vertical position Dpx. Meanwhile, ifthe magnitude of the vertical position difference ΔDx is small, thesurrounding monitoring ECU 20 determines that the error of the verticalposition Dx is small and uses the vertical position Dx as the processedvertical position Dpx.

Similarly, when the surrounding monitoring ECU 20 executes the positioncorrection process, if the horizontal position difference ΔDy is greaterthan a predetermined first horizontal limit value Dyth1 (i.e.,ΔDy>Dyth1>0), the surrounding monitoring ECU 20 determines the processedhorizontal position Dpy to be equal to a value obtained by adding thefirst horizontal limit value Dyth1 to the previous horizontal positionDoy (i.e., Dpy←Doy+Dyth1). For convenience, the value obtained by addingthe first horizontal limit value Dyth1 to the previous horizontalposition Doy will also be referred to as a “first specific value.”

If the horizontal position difference ΔDy is smaller than a value(−Dyth2) obtained by multiplying a predetermined second horizontal limitvalue Dyth2 by “−1” (i.e., ΔDy<−Dyth2<0), the surrounding monitoring ECU20 determines the processed horizontal position Dpy to be equal to avalue obtained by subtracting the second horizontal limit value Dyth2from the previous horizontal position Doy (i.e., Dpy←Doy−Dyth2). Forconvenience sake, the value obtained by subtracting the secondhorizontal limit value Dyth2 from the previous horizontal position Doywill also be referred to as a “second specific value.”

If the horizontal position difference ΔDy is equal to or smaller thanthe first horizontal limit value Dyth1 and equal to or larger than thevalue obtained by multiplying the second horizontal limit value Dyth2 by“−1” (i.e., −Dyth2≤ΔDy≤Dyth1), the surrounding monitoring ECU 20determines the processed horizontal position Dpy to be equal to thehorizontal position Dy (i.e., Dpy←Dy).

In the present embodiment, all the first vertical limit value Dxth1, thesecond vertical limit value Dxth2, the first horizontal limit valueDyth1, and the second horizontal limit value Dyth2 are equal to adistance threshold Dth. Notably, some of or all the first vertical limitvalue Dxth1, the second vertical limit value Dxth2, the first horizontallimit value Dyth1, and the second horizontal limit value Dyth2 maydiffer from one another.

Incidentally, if the moving speed of the pedestrian does not change, asthe magnitude |Vs| of the vehicle speed Vs increases, the magnitude|ΔDx| of the vertical position difference ΔDx and the magnitude |ΔDy| ofthe horizontal position difference ΔDy increase. In view of this, thesurrounding monitoring ECU 20 sets the distance threshold Dth (i.e., thefirst vertical limit value Dxth1, the second vertical limit value Dxth2,the first horizontal limit value Dyth1, and the second horizontal limitvalue Dyth2) such that the larger the magnitude |Vs| of the vehiclespeed Vs, the larger the distance threshold Dth. FIG. 4 shows therelation between the vehicle speed Vs and the distance threshold Dth. Ascan be understood from FIG. 4, when the vehicle speed Vs is “0,” thedistance threshold Dth is a distance D1. As the vehicle speed Vsdecreases in the range smaller than “0,” the distance threshold Dthincreases.

The above-mentioned position correction process will be described morespecifically with reference to FIG. 5. FIG. 5 shows examples of changesin the actual x coordinate value of the pedestrian position, thevertical position Dx obtained by the position obtainment process, andthe processed vertical position Dpx obtained by the position correctionprocess with elapse of time t, wherein the changes were determined attime intervals Ts from time t0 to t12. In the example of FIG. 5, the xcoordinate value of the pedestrian decreases with elapse of time.Notably, since the position correction process for the horizontalposition Dy is the same as the position correction process for thevertical position Dx, description for the horizontal position Dy withreference to a chart similar to the chart of FIG. 5 is omitted.

At time t4 of FIG. 5, the actual x coordinate value of the pedestrian isx4 a. The vertical position Dx obtained by the position obtainmentprocess at time t4 is x4 b approximately equal to x4 a (i.e., Dx=x4 b≅x4a). In addition, the processed vertical position Dpx obtained by theposition correction process at time t4 is x4 c equal to the verticalposition Dx (=x4 b) (i.e., Dpx=x4 c=x4 b).

At time t5 after elapse of the time interval Ts from time t4, the actualx coordinate value of the pedestrian is x5 a. Meanwhile, since thecontour extraction error in the position obtainment process executed attime t5 was large, the vertical position Dx is x5 b which is smallerthan the actual x coordinate value x5 a (i.e., Dx=x5 b<x5 a). As aresult, the vertical position difference ΔDx at time t5 is smaller thanthe value obtained by multiplexing the second vertical limit value Dxth2by “−1” (i.e., ΔDx=x5 b−x4 c<−Dxth2). Therefore, the processed verticalposition Dpx obtained by the position correction process at time t5becomes x5 c which is a value obtained by subtracting the secondvertical limit value Dxth2 from the previous vertical position Dox (inthis case, x4 c which is the processed vertical position Dpx at time t4)(i.e., Dpx=x5 c=x4 c−Dxth2).

At time t6 after elapse of the time interval Ts from time t5, the actualx coordinate value of the pedestrian is x6 a. Meanwhile, the verticalposition Dx obtained by the position obtainment process at time t6 is x6b approximately equal to x6 a (i.e., Dx=x6 b≅x6 a). The verticalposition difference ΔDx at time t6 (=x6 b−x5 c) is equal to or smallerthan the first horizontal limit value Dyth1 and the vertical positiondifference ΔDx is equal to or larger than the value (−Dyth2) obtained bymultiplexing the second horizontal limit value Dyth2 by “−1” (i.e.,−Dyth2≤ΔDx≤Dyth1). Therefore, the processed vertical position Dpxobtained by the position correction process at time t6 is x6 c equal tothe vertical position Dx (=x6 b) (i.e., Dpx=x6 c=x6 b).

At time t9, the actual x coordinate value of the pedestrian is x9 a, thevertical position Dx is x9 b approximately equal to x9 a (i.e., Dx=x9b≅x9 a), and the processed vertical position Dpx is x9 c equal to thevertical position Dx (=x9 b) (i.e., Dpx=x9 c=x9 b).

At time t10 after elapse of the time interval Ts from time t9, theactual x coordinate value of the pedestrian is x10 a. Meanwhile, sincethe contour extraction error in the position obtainment process executedat time t10 was large, the vertical position Dx is x10 b which is largerthan the actual x coordinate value x10 a (i.e., Dx=x10 b>x10 a). As aresult, the vertical position difference ΔDx at time t10 is larger thanthe first vertical limit value Dxth1 (i.e., ΔDx=x10 b−x9 c>Dxth1).Therefore, the processed vertical position Dpx obtained by the positioncorrection process becomes x10 c which is a value obtained by adding thefirst vertical limit value Dxth1 to the previous vertical position Dox(in this case, x9 c which is the processed vertical position Dpx at timet9) (i.e., Dpx=x10 c=x9 c+Dxth1).

At time t11 after elapse of the time interval Ts from time t10, theactual x coordinate value of the pedestrian is x11 a. The verticalposition Dx obtained by the position obtainment process at time t11 isx11 b approximately equal to x11 a (i.e., Dx=x11 b≅x11 a). The verticalposition difference ΔDx at time t11 is smaller than the value (−Dyth2)obtained by multiplexing the second horizontal limit value Dyth2 by “−1”(i.e., ΔDx=x11 b−x10 c<−Dxth2). Therefore, the processed verticalposition Dpx obtained by the position correction process at time t11 isx11 c which is a value obtained by subtracting the second vertical limitvalue Dxth2 from the previous vertical position Dox (in this case, x10 cwhich is the processed vertical position Dpx at time t10) (i.e., Dpx=x11c=x10 c−Dxth2).

At time t12 after elapse of the time interval Ts from time t11, theactual x coordinate value of the pedestrian is x12 a. Meanwhile, thevertical position Dx obtained by the position obtainment process at timet12 is x12 b approximately equal to x12 a (i.e., Dx=x12 b≅x12 a). Thevertical position difference ΔDx at time t12 (=x12 b−x11 c) is equal toor smaller than the first horizontal limit value Dyth1 and the verticalposition difference ΔDx is equal to or larger than the value (−Dyth2)obtained by multiplexing the second horizontal limit value Dyth2 by “−1”(i.e., −Dyth2≤ΔDx≤Dyth1). Therefore, the processed vertical position Dpxobtained by the position correction process at time t12 is x12 c equalto the vertical position Dx (=x12 b) (i.e., Dpx=x12 c=x12 b).

After having obtained the processed vertical position Dpx and theprocessed horizontal position Dpy corresponding to the pedestriancontained in the heading direction image by the position obtainmentprocess and the position correction process, the surrounding monitoringECU 20 determines whether or not that pedestrian is a “pedestrian onpath.” The pedestrian on path is a pedestrian who is highly likely tocollide with the vehicle 10 when the vehicle 10 moves backward.

The surrounding monitoring ECU 20 determines that the pedestrian is a“pedestrian on path” when either one or both of the following conditions(A) and (B) are satisfied.

-   (A) The pedestrian is present in a path region Ap at the present    point in time.-   (B) The pedestrian is present in the path region Ap after elapse of    a predetermined prediction time Tf (2 seconds in the present    embodiment) from the present point in time.

FIG. 6 shows the path region Ap when the steering angle θs is “0.” Asshown in FIG. 6, the path region Ap extends rearward from the vehicle10, has a center coinciding with the center axis Cs, and has a widthwhich is equal to the sum of the width Lw of the vehicle 10 and avehicle width margin Lm. Namely, the path region Ap is a region betweena straight line LL and a straight line LR. The straight line LL passesthrough a point PL offset leftward from the position of the left sidesurface of a rear end portion of the vehicle 10 by a half (Lm/2) of thevehicle width margin Lm and extends backward from the rear end of thevehicle 10 parallel to the center axis Cs. The straight line LR passesthrough a point PR offset rightward from the position of the right sidesurface of the rear end portion of the vehicle 10 by a half (Lm/2) ofthe vehicle width margin Lm and extends backward from the rear end ofthe vehicle 10 parallel to the center axis Cs.

Meanwhile, when the steering angle θs is not “0,” the path region Apcurves leftward or rightward in accordance with the steering angle θs.Specifically, when the steering angle θs is negative, as shown in FIG.7, as the degree of separation from the vehicle 10 increases, therightward deviation of the lateral center of the path region Ap from thecenter axis Cs increases (namely, as the x coordinate value increases,the y coordinate value of the right end of the path region Apdecreases). In the case, the path region Ap is a region between a leftside arc YL passing through the point PL and a right side arc YR passingthrough the point PR. Meanwhile, when the steering angle θs is positive,the path region Ap is defined in such a manner that, as the degree ofseparation from the vehicle 10 increases, the leftward deviation of thelateral center of the path region Ap from the center axis Cs increases(namely, as the x coordinate value increases, the y coordinate value ofthe left end of the path region Ap increases).

When the position represented by the processed vertical position Dpx andthe processed horizontal position Dpy is contained in the path regionAp, the surrounding monitoring ECU 20 determines that theabove-described condition (A) is satisfied. Further, in order todetermine whether or not the above-described condition (B) is satisfied,the surrounding monitoring ECU 20 obtains a predicted vertical positionDfx which is a predicted value of the x coordinate value of thepedestrian at the time after elapse of the prediction time Tf from thepresent point in time. In addition, the surrounding monitoring ECU 20obtains a predicted horizontal position Dfy which is a predicted valueof the y coordinate value of the pedestrian at the time after elapse ofthe prediction time Tf from the present point in time. If the positionrepresented by the predicted vertical position Dfx and the predictedhorizontal position Dfy is contained in the path region Ap, thesurrounding monitoring ECU 20 determines that the above-describedcondition (B) is satisfied.

For convenience sake, the process executed by the surrounding monitoringECU 20 so as to obtain the predicted vertical position Dfx and thepredicted horizontal position Dfy will also be referred to as a“position prediction process.” At the time of execution of the positionprediction process, the surrounding monitoring ECU 20 obtains a verticalvelocity Vx which is the velocity component of the pedestrian in thevertical direction (the x-axis direction) and a horizontal velocity Vywhich is the velocity component of the pedestrian in the horizontaldirection (the y-axis direction).

Specifically, the surrounding monitoring ECU 20 calculates the verticalvelocity Vx by dividing the vertical position difference ΔDx by the timeinterval Ts (i.e., Vx=ΔDx/Ts). Similarly, the surrounding monitoring ECU20 calculates the horizontal velocity Vy by dividing the horizontalposition difference ΔDy by the time interval Ts (i.e., Vy=ΔDy/Ts).

The surrounding monitoring ECU 20 calculates the predicted verticalposition Dfx by adding to the processed vertical position Dpx a “valueobtained by multiplying the “vertical velocity Vx by the prediction timeTf” (i.e., Dfx←Dpx+Vx×Tf). Similarly, the surrounding monitoring ECU 20calculates the predicted horizontal position Dfy by adding to theprocessed horizontal position Dpy a “value obtained by multiplying the“horizontal velocity Vy by the prediction time Tf” (i.e.,Dfy←Dpy+Vy×Tf).

If a pedestrian on path is present (namely, the above-describedcondition (A) and/or condition (B) is satisfied), the surroundingmonitoring ECU 20 calculates a required deceleration Dcreq which is anacceleration As required for the vehicle 10 to stop before thepedestrian on path. Since the required deceleration Dcreq is anacceleration As determined such that when the vehicle 10 is movingbackward (namely, when Vs<0), the magnitude |Vs| of the vehicle speed Vsdecreases, the required deceleration Dcreq assumes a positive value(i.e., Dcreq>0).

Specifically, the surrounding monitoring ECU 20 calculates the requireddeceleration Dcreq in accordance with the following Equation (1) as theacceleration As required to stop the vehicle 10 after the vehicle 10travels over a travel distance Dd.Dcreq=(½)·Vs ² /Dd  (1)

The surrounding monitoring ECU 20 calculates the difference between apredetermined length (stop position margin) Lv and a travel distance(journey) Dw of the vehicle 10 before collision with the pedestrian onpath for the case where the steering angle θs is assumed to be constant,and calculates the required deceleration Dcreq by substituting thedifference into Equation (1) as the travel distance Dd (i.e., Dd=Dw−Lv).If the required deceleration Dcreq is greater than a predeterminedacceleration threshold Ath (i.e., Dcreq>Ath), the surrounding monitoringECU 20 determines that the possibility of collision of the vehicle 10with the pedestrian on path is high.

When the surrounding monitoring ECU 20 determines that the possibilityof collision of the vehicle 10 with the pedestrian on path is high, thesurrounding monitoring ECU 20 notifies (warns) the driver of the vehicle10, through the input output device 46 and the speakers 47, the factthat the possibility of collision with the pedestrian on path is high.In addition, the surrounding monitoring ECU 20 executes an “automaticbraking process” of sending request signals to the engine ECU 31 and thebrake ECU 32 such that the actual acceleration As becomes equal to therequired deceleration Dcreq.

Specifically, the surrounding monitoring ECU 20 sends a request signalto the brake ECU 32 so as to request the brake ECU 32 to generate abraking force Bf for making the actual acceleration As equal to therequired deceleration Dcreq. In addition, the surrounding monitoring ECU20 sends a request signal to the engine ECU 31 so as to request theengine ECU 31 to decrease the drive torque Tq to “0.” As a result, themagnitude |Vs| of the vehicle speed Vs decreases and finally becomes“0.”

Specific Operation

Next, specific operation of the surrounding monitoring ECU 20 will bedescribed. The CPU of the surrounding monitoring ECU 20 (hereinafter maybe referred to as the “CPU” for simplification) executes a “collisionavoidance control routine” represented by a flowchart in FIG. 8 everytime the time interval Ts elapses.

Accordingly, when a proper timing has come, the CPU starts the processfrom step 800 of FIG. 8 and proceeds to step 805 so as to determinewhether or not a collision avoidance control requested flag is in an ONstate. In the case where the collision avoidance control requested flaghas been set to an OFF state as a result of a driver's operation of theinput output device 46, the CPU makes a “No” determination in step 805and proceeds directly to step 895 so as to end the current execution ofthe present routine.

Meanwhile, in the case where the collision avoidance control requestedflag is in the ON state, the CPU makes a “Yes” determination in step 805and proceeds to step 810 so as to determine whether or not the automaticbraking process has already been started. In the case where theautomatic braking process has not yet been started, the CPU makes a“Yes” determination in step 810 and proceeds to step 815 so as todetermine whether or not the shift position detected by the shiftposition sensor 41 is the reverse (R) range.

In the case where the shift position is the reverse (R) range, the CPUmakes a “Yes” determination in step 815 and proceeds to step 820 so asto determine whether or not a pedestrian(s) is contained in the headingdirection image. In the case where a pedestrian(s) is contained in theheading direction image, the CPU makes a “Yes” determination in step 820and proceeds to step 825. In step 825, the CPU executes the positionobtainment process to thereby obtain the vertical position Dx and thehorizontal position Dy of a “particular pedestrian among the pedestrianscontained in the heading direction image.” Subsequently, the CPUproceeds to step 830 so as to obtain the processed vertical position Dpxand the processed horizontal position Dpy of the pedestrian by executinga “position correction process routine” represented by a flowchart inFIG. 9. The position correction process routine” shown in FIG. 9 will bedescribed later.

After execution of the “position correction process routine” of FIG. 9,the CPU proceeds to step 835 so as to execute the position predictionprocess to thereby obtain the predicted vertical position Dfx and thepredicted horizontal position Dfy. Further, the CPU proceeds to step 840so as to determine whether or not the pedestrian is a pedestrian onpath. Specifically, the CPU determines whether or not theabove-described condition (A) and/or condition (B) is satisfied.

In the case where the condition (A) and/or the condition (B) issatisfied, the CPU makes a “Yes” determination in step 840 and proceedsto step 845. In step 845, the CPU obtains the required decelerationDcreq in accordance with the above-described Equation (1) and stores therequired deceleration Dcreq in the RAM while relating it with theparticular pedestrian. Next, the CPU proceeds to step 850.

Meanwhile, in the case where none of the condition (A) and the condition(B) is satisfied, the CPU makes a “No” determination in step 840 andproceeds directly to step 850.

In step 850, the CPU determines whether or not the above-describedprocess has been performed for all the pedestrians contained in theheading direction image. In the case where a pedestrian(s) for which theabove-described process has not yet been performed remains, the CPUmakes a “No” determination in step 850 and proceeds to step 825 afterselecting a different pedestrian.

Meanwhile, in the case where the above-described process has beenperformed for all the pedestrians contained in the heading directionimage, the CPU makes a “Yes” determination in step 850 and proceeds tostep 855 so as to determine whether or not a pedestrian on path ispresent and the required deceleration Dcreq is greater than theacceleration threshold Ath. In the case where a plurality of requireddecelerations Dcreq have been obtained because of presence of aplurality of pedestrians on path, the CPU compares the maximum requireddeceleration Dcreq with the acceleration threshold Ath.

In the case where a pedestrian on path is present and the requireddeceleration Dcreq (or the maximum required deceleration Dcreq) isgreater than the acceleration threshold Ath, the CPU makes a “Yes”determination in step 855 and proceeds to step 860 so as to notify thedriver of the vehicle 10 that the possibility of collision with thepedestrian present in the backward direction of the vehicle 10 is high.Specifically, the CPU causes the input output device 46 to display asymbol which indicates that the possibility of collision with thepedestrian is high and causes the speakers 47 to reproduce a warningsound.

Next, the CPU proceeds to step 865 so as to start the automatic brakingprocess. More specifically, the CPU transmits the required decelerationDcreq to the brake ECU 32 through the CAN 34. In the case where aplurality of the required decelerations Dcreq have been obtained, theCPU transmits the maximum required deceleration Dcreq to the brake ECU32. As a result, the brake ECU 32 controls the brake actuator 66 byexecuting an unillustrated routine such that the actual acceleration Asbecomes equal to the required deceleration Dcreq, whereby the requiredbraking force Bf is generated.

Further, the CPU sets the value of the target drive torque Tqtgt to “0”and transmits the target drive torque Tqtgt to the engine ECU 31 throughthe CAN 34. As a result, the engine ECU 31 controls the engine actuators63 and the transmission 64 by executing an unillustrated routine suchthat the actual drive torque Tq becomes equal to the target drive torqueTqtgt. Subsequently, the CPU proceeds to step 895.

Notably, in the case where the determination condition of step 810 isnot satisfied (i.e., in the case where the automatic braking process hasalready been started), the CPU makes a “No” determination in step 810and proceeds directly to step 895. Further, in the case where thedetermination condition of step 815 is not satisfied (i.e., in the casewhere the shift position is not the reverse (R) range), the CPU makes a“No” determination in step 815 and proceeds directly to step 895.

In addition, in the case where the determination condition of step 820is not satisfied (i.e., in the case where the heading direction imagecontains no pedestrian), the CPU makes a “No” determination in step 820and proceeds directly to step 895. Further, in the case where thedetermination condition of step 855 is not satisfied (i.e., in the casewhere the required deceleration Dcreq is equal to or less than theacceleration threshold Ath), the CPU makes a “No” determination in step855 and proceeds directly to step 895.

Notably, in the case where a predetermined end condition is satisfiedduring execution of the automatic braking process, the CPU ends theautomatic braking process and the notification to the driver through theinput output device 46 and the speakers 47 by executing an unillustratedroutine. The condition for ending the automatic braking process is acondition which is satisfied when the vehicle speed Vs becomes “0”and/or when the magnitude of change in the steering angle θs duringexecution of the automatic braking process becomes greater than apredetermined threshold.

Next, the “position correction process routine” will be described. Whenthe CPU proceeds to step 830 of FIG. 8, the CPU starts the process fromstep 900 of FIG. 9 and proceeds to step 905 so as to calculate thevertical position difference ΔDx and the horizontal position differenceΔDy.

More specifically, the CPU obtains the vertical position difference ΔDxby subtracting the previous vertical position Dox from the verticalposition Dx obtained when step 825 of FIG. 8 was executed latest. Theprevious vertical position Dox is the value which was stored in the RAMby the process of step 960 (to be described later) when the presentroutine was executed last time. Similarly, the CPU obtains thehorizontal position difference ΔDy by subtracting the previoushorizontal position Doy from the horizontal position Dy obtained whenstep 825 was executed latest. The previous horizontal position Doy isthe value which was stored in the RAM by the process of step 960 whenthe present routine was executed last time.

Next, the CPU proceeds to step 910 so as to determine whether or not thevertical position difference ΔDx is larger than the first vertical limitvalue Dxth1. In the case where the vertical position difference ΔDx islarger than the first vertical limit value Dxth1, the CPU makes a “Yes”determination in step 910 and proceeds to step 915 so as to calculate(determine) the processed vertical position Dpx by adding the firstvertical limit value Dxth1 to the previous vertical position Dox.Subsequently, the CPU proceeds to step 935.

Meanwhile, in the case where the vertical position difference ΔDx isequal to or smaller than the first vertical limit value Dxth1, the CPUmakes a “No” determination in step 910 and proceeds to step 920 so as todetermine whether or not the vertical position difference ΔDx is smallerthan the value obtained by multiplying the second vertical limit valueDxth2 by “−1.” In the case where the vertical position difference ΔDx issmaller than the value obtained by multiplying the second vertical limitvalue Dxth2 by “−1,” the CPU makes a “Yes” determination in step 920 andproceeds to step 925 so as to calculate (determine) the processedvertical position Dpx by subtracting the second vertical limit valueDxth2 from the previous vertical position Dox. Subsequently, the CPUproceeds to step 935.

In the case where the vertical position difference ΔDx is equal to orlarger than the value obtained by multiplying the second vertical limitvalue Dxth2 by “−1,” the CPU makes a “No” determination in step 920 andproceeds to step 930 so as to determine the processed vertical positionDpx such that the processed vertical position Dpx becomes equal to thevertical position Dx. Subsequently, the CPU proceeds to step 935.

In step 935, the CPU determines whether or not the horizontal positiondifference ΔDy is larger than the first horizontal limit value Dyth1. Inthe case where the horizontal position difference ΔDy is larger than thefirst horizontal limit value Dyth1, the CPU makes a “Yes” determinationin step 935 and proceeds to step 940 so as to calculate (determine) theprocessed horizontal position Dpy by adding the first horizontal limitvalue Dyth1 to the previous horizontal position Doy. Subsequently, theCPU proceeds to step 960.

Meanwhile, in the case where the horizontal position difference ΔDy isequal to or smaller than the first horizontal limit value Dyth1, the CPUmakes a “No” determination in step 935 and proceeds to step 945 so as todetermine whether or not the horizontal position difference ΔDy issmaller than the value obtained by multiplying the second horizontallimit value Dyth2 by “−1.” In the case where the horizontal positiondifference ΔDy is smaller than the value obtained by multiplying thesecond horizontal limit value Dyth2 by “−1,” the CPU makes a “Yes”determination in step 945 and proceeds to step 950 so as to calculate(determine) the processed horizontal position Dpy by subtracting thesecond horizontal limit value Dyth2 from the previous horizontalposition Doy. Subsequently, the CPU proceeds to step 960.

In the case where the horizontal position difference ΔDy is equal to orlarger than the value obtained by multiplying the second horizontallimit value Dyth2 by “−1,” the CPU makes a “No” determination in step945 and proceeds to step 955 so as to determine the processed horizontalposition Dpy such that the processed horizontal position Dpy becomesequal to the horizontal position Dy. Subsequently, the CPU proceeds tostep 960.

In step 960, the CPU stores the processed vertical position Dpx in theRAM as the previous vertical position Dox and stores the processedhorizontal position Dpy in the RAM as the previous horizontal positionDoy. Subsequently, the CPU proceeds to step 995 so as to end the presentroutine. Namely, the CPU proceeds to step 835 of FIG. 8.

As having been described above, even when the error in extraction of thecontour of the pedestrian contained in the heading direction imagecaptured by the rear camera 45 becomes large temporarily, the“positional relation between the vehicle 10 and a pedestrian (thevertical position and the horizontal position of the pedestrian)”recognized by the present monitoring apparatus can be prevented fromgreatly deviating from the actual positional relation. Therefore, thepresent monitoring apparatus can accurately determine whether or not thepossibility of collision of the vehicle 10 with the pedestrian is high.

The embodiment of the vehicle surrounding monitoring apparatus accordingto the present invention has been described; however, the presentinvention is not limited to the above-described embodiment, and variousmodifications are possible without departing from the scope of theinvention. For example, the surrounding monitoring ECU 20 according tothe present embodiment executes the collision avoidance control when thevehicle 10 moves backward. However, the surrounding monitoring ECU 20may execute the collision avoidance control when the vehicle 10 movesforward. In this case, the vehicle 10 includes an onboard camera (frontcamera) for capturing an image of a front region, and the front cameraoutputs to the surrounding monitoring ECU 20 a signal representing thecaptured image (heading direction image).

The surrounding monitoring ECU 20 according to the present embodimentexecutes the position correction process for both the vertical positionDx and the horizontal position Dy. However, the surrounding monitoringECU 20 may execute the position correction process for only one of thevertical position Dx and the horizontal position Dy. For example, in thecase where the surrounding monitoring ECU 20 executes the positioncorrection process for the vertical position Dx only, the surroundingmonitoring ECU 20 uses, as the processed horizontal position Dpy, thehorizontal position Dy obtained by the position obtainment process asis.

The surrounding monitoring ECU 20 according to the present embodimentobtains the vertical position Dx and the horizontal position Dy of eachpedestrian by executing the position obtainment process. However,instead of the vertical position Dx and the horizontal position Dy, thesurrounding monitoring ECU 20 may obtain the angle of the pedestrianwith respect to the vehicle 10 (the angle between the center axis Cs anda straight line connecting the origin and the position of thepedestrian) θv and the direct distance Dv between the origin and theposition of the pedestrian. In this case, the surrounding monitoring ECU20 may execute the position correction process such that the magnitudeof change in the angle θv per time interval Ts does not exceed apredetermined angle threshold. In addition, the surrounding monitoringECU 20 may execute the position correction process such that the amountof change in the direct distance Dv per time interval Ts does not exceeda predetermined distance threshold.

As shown in FIG. 4, the surrounding monitoring ECU 20 according to thepresent embodiment changes the distance threshold Dth (i.e., the firstvertical limit value Dxth1, the second vertical limit value Dxth2, thefirst horizontal limit value Dyth1, and the second horizontal limitvalue Dyth2) in accordance with the vehicle speed Vs. However, some ofor all the first vertical limit value Dxth1, the second vertical limitvalue Dxth2, the first horizontal limit value Dyth1, and the secondhorizontal limit value Dyth2 may be fixed values irrespective of thevehicle speed Vs.

The surrounding monitoring ECU 20 according to the present embodimentdetermines that a pedestrian satisfying either one or both of thecondition (A) and the condition (B) is a pedestrian on path. However,the process of determining whether or not the pedestrian satisfies thecondition (B) may be omitted.

The surrounding monitoring ECU 20 according to the present embodimentdetermines that when the required deceleration Dcreq is greater than theacceleration threshold Ath, the possibility of collision with thepedestrian on path is high. However, the surrounding monitoring ECU 20may determine whether or not the possibility of collision with thepedestrian on path is high by a method different from the methodemployed in the embodiment. For example, the surrounding monitoring ECU20 may obtain a time (time to collision) until the vehicle 10 collideswith the pedestrian on path under the assumption that the vehicle speedVs is constant, and determine that the possibility of collision with thepedestrian on path is high if the time to collision is shorter than apredetermined time.

In the present embodiment, no limitation is imposed on the length of thepath region Ap. However, the path region Ap extending rearward from thevehicle 10 may have a limited length. In this case, when a pedestrian onpath contained in the path region Ap is present, the surroundingmonitoring ECU 20 may determine that the possibility of collision of thevehicle 10 with the pedestrian on path is high without calculating therequired deceleration Dcreq.

In the present embodiment, when the surrounding monitoring ECU 20determines that the possibility of collision of the vehicle 10 with thepedestrian on path is high, the surrounding monitoring ECU 20 controlsthe engine ECU 31 and the brake ECU 32 such that the actual accelerationAs becomes equal to the required deceleration Dcreq. However, when thesurrounding monitoring ECU 20 determines that the possibility ofcollision of the vehicle 10 with the pedestrian on path is high, thesurrounding monitoring ECU 20 may control the brake ECU 32 such that thebrake actuator 66 generates the “maximum frictional braking force withina range within which no slippage occurs between a road surface and thewheels of the vehicle 10” irrespective of the value of the requireddeceleration Dcreq.

The surrounding monitoring ECU 20 according to the present embodimentobtains the vertical position Dx and the horizontal position Dy of eachpedestrian by executing the position obtainment process. However, theposition obtainment process may be executed by an apparatus differentfrom the surrounding monitoring ECU 20 (for example, a camera ECU). Inthis case, the surrounding monitoring ECU 20 receives from the cameraECU a signal representing the vertical position Dx and the horizontalposition Dy of each pedestrian.

When the surrounding monitoring ECU 20 according to the presentembodiment determines that the possibility of collision with apedestrian is high, the surrounding monitoring ECU 20 executes theautomatic braking process and the notification (warning) to the driverof the vehicle 10. However, one of the notification to the driver andthe automatic braking process may be omitted.

What is claimed is:
 1. A surrounding monitoring apparatus comprising:one camera which is mounted on a vehicle and which obtains a headingdirection image by photographing a region in a heading direction of saidvehicle; and an electronic control unit which is implemented by at leastone programmed processor and which is configured to realize a pedestrianposition obtainment step, a position processing step, and a collisiondetermination step, wherein said pedestrian position obtainment stepwhich executes a position obtainment process every time a predeterminedtime interval elapses so as to obtain a position correlation valuerepresenting a position of a pedestrian with respect to said vehicle onthe basis of a position of said pedestrian in said heading directionimage; said position processing step which operates every time saidposition correlation value is obtained so as to determine a positionprocessed value on the basis of said obtained position correlationvalue; and said collision determination step which determines, at afirst time point when said position processed value is newly determined,whether or not a possibility of collision of said vehicle with saidpedestrian is high on the basis of said newly determined positionprocessed value, wherein said position processing step is configuredsuch that when said position correlation value obtained at said firsttime point is larger than a first specific value obtained by adding apredetermined first limit value to said position processed value at asecond time point which precedes said first time point by said timeinterval, said position processing step sets said position processedvalue at said first time point to be equal to said first specific value;when said position correlation value obtained at said first time pointis smaller than a second specific value obtained by subtracting apredetermined second limit value from said position processed value atsaid second time point, said position processing step sets said positionprocessed value at said first time point to be equal to said secondspecific value; and when said position correlation value obtained atsaid first time point is equal to or smaller than said first specificvalue and is equal to or larger than said second specific value, saidposition processing step sets said position processed value at saidfirst time point to be equal to said position correlation value obtainedat said first time point.
 2. A surrounding monitoring apparatusaccording to claim 1, wherein said position processing step isconfigured to change at least one of said first limit value and saidsecond limit value such that said at least one limit value increaseswith the magnitude of travel speed of said vehicle.
 3. A surroundingmonitoring apparatus according to claim 1, wherein said camera isconfigured to obtain said heading direction image such that the longerthe distance between said vehicle and an object present in said headingdirection, the higher the position of said object in said headingdirection image; and said pedestrian position obtainment step isconfigured to obtain, as said position correlation value, a valuerepresenting the distance between said vehicle and said pedestrian insaid vehicle heading direction, and is configured to obtain saidposition correlation value such that the higher the position of a footof said pedestrian in said heading direction image, the greater saiddistance represented by said position correlation value.
 4. Asurrounding monitoring apparatus according to claim 1, wherein saidcollision determination step is configured to employ, as a necessarycondition for determining that the possibility of collision of saidvehicle with said pedestrian is high, a condition that said positionprocessed value is a value representing a position within a path regionthrough which said vehicle is expected to pass as a result of traveling.5. A surrounding monitoring apparatus according to claim 2, wherein saidcollision determination step is configured to employ, as a necessarycondition for determining that the possibility of collision of saidvehicle with said pedestrian is high, a condition that said positionprocessed value is a value representing a position within a path regionthrough which said vehicle is expected to pass as a result of traveling.6. A surrounding monitoring apparatus according to claim 3, wherein saidcollision determination step is configured to employ, as a necessarycondition for determining that the possibility of collision of saidvehicle with said pedestrian is high, a condition that said positionprocessed value is a value representing a position within a path regionthrough which said vehicle is expected to pass as a result of traveling.7. A surrounding monitoring apparatus according to claim 1, wherein saidcollision determination step is configured to estimate, on the basis ofsaid position processed value, a predicted position which is theposition of said pedestrian with respect to said vehicle after elapse ofa predetermined prediction time.
 8. A surrounding monitoring apparatusaccording to claim 2, wherein said collision determination step isconfigured to estimate, on the basis of said position processed value, apredicted position which is the position of said pedestrian with respectto said vehicle after elapse of a predetermined prediction time, and toemploy, as a necessary condition for determining that the possibility ofcollision of said vehicle with said pedestrian is high, a condition thatsaid predicted position is a position within a path region through whichsaid vehicle is expected to pass as a result of traveling.
 9. Asurrounding monitoring apparatus according to claim 3, wherein saidcollision determination step is configured to estimate, on the basis ofsaid position processed value, a predicted position which is theposition of said pedestrian with respect to said vehicle after elapse ofa predetermined prediction time, and to employ, as a necessary conditionfor determining that the possibility of collision of said vehicle withsaid pedestrian is high, a condition that said predicted position is aposition within a path region through which said vehicle is expected topass as a result of traveling.
 10. A surrounding monitoring apparatusaccording to claim 4, wherein said collision determination step isconfigured to estimate, on the basis of said position processed value, apredicted position which is the position of said pedestrian with respectto said vehicle after elapse of a predetermined prediction time, and toemploy, as a necessary condition for determining that the possibility ofcollision of said vehicle with said pedestrian is high, a condition thatsaid predicted position is a position within a path region through whichsaid vehicle is expected to pass as a result of traveling.
 11. Asurrounding monitoring apparatus according to claim 5, wherein saidcollision determination step is configured to estimate, on the basis ofsaid position processed value, a predicted position which is theposition of said pedestrian with respect to said vehicle after elapse ofa predetermined prediction time, and to employ, as a necessary conditionfor determining that the possibility of collision of said vehicle withsaid pedestrian is high, a condition that said predicted position is aposition within a path region through which said vehicle is expected topass as a result of traveling.
 12. A surrounding monitoring apparatusaccording to claim 6, wherein said collision determination step isconfigured to estimate, on the basis of said position processed value, apredicted position which is the position of said pedestrian with respectto said vehicle after elapse of a predetermined prediction time, and toemploy, as a necessary condition for determining that the possibility ofcollision of said vehicle with said pedestrian is high, a condition thatsaid predicted position is a position within a path region through whichsaid vehicle is expected to pass as a result of traveling.